Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$178.80	4.720%	$187.2394	$187.24	$187.25	$187.20
Purchase #2	$94.70	11.173%	$105.2808	$105.28	$105.30	$105.30
Purchase #3	$153.25	12.126%	$171.8331	$171.83	$171.85	$171.80
Purchase #4	$118.41	10.153%	$130.4322	$130.43	$130.45	$130.40
Purchase #5	$46.54	9.220%	$50.831	$50.83	$50.85	$50.80
Purchase #6	$15.46	6.376%	$16.4457	$16.45	$16.45	$16.40
Purchase #7	$140.75	11.864%	$157.4486	$157.45	$157.45	$157.40
7 purchase totals =	$747.91		$819.5108	$819.51	$819.60	$819.30